What mass of hydrochloric acid is needed to decompose 50 g of limestone?

$\underset{100 \mathrm{g}}{{\mathrm{CaCO}}_3}+2\mathrm{HCl}\to \underset{2\mathrm{x}36.5=73\mathrm{g}}{{\mathrm{CaCl}}_2}+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2$
100 g of CaCO₃ requires 73 g of HCI
$\therefore$ 50 g of CaCO₃ requires $\frac{73}{100} \times 50=36.5 \mathrm{g} \mathrm{of} \mathrm{HCl}$